1. Field of Invention
The present invention concerns a method and apparatus for improving the leveling requirements of an elevator system. In particular, the invention provides a method and apparatus for reducing the required leveling by predicting the suspended load on the elevator's tension members.
2. Background of Invention
Accurate leveling between the floor of an elevator car and the landing at which the elevator is located, is an essential requirement for the safe operation of elevators. Specifications and industry standards require that elevators maintain a level difference between the elevator car floor and landing floor of within ⅜″.
Elevators are generally suspended by tension members that stretch and change length. The amount by which the tension members may change in length depends on the suspended load, where the load is the weight of the elevator car, plus the weight of its contents (e.g., one or more persons). As the weight of the suspended load increases due to passengers entering the elevator car, the length of the suspension members increases as a result of stretching. Similarly, when the suspended load decreases (e.g., due to passengers leaving the elevator car), the length of the suspension members decreases.
If the magnitude of these changes in rope length cause the level difference between the elevator car floor and landing floor to exceed the ⅜″ level requirement, the elevator re-levels. Re-leveling can be disconcerting to passengers and may even cause them to loose their balance. Therefore, while re-leveling is unavoidable, it should be minimized where possible. It is therefore an object of the present invention to minimize re-leveling in elevator systems.